I found the culprit for this: it ends up that I have used old key and base URL (before integration with windy.com). It worked fine few months but not any more. With new key and new base URL: https://api.windy.com/api/webcams/v2/, everything works fine.
Okay, I think I misunderstood the the response data. I'm guessing total refers to the total number of webcams, and the regions field lists all of the available regions. In which case, this is definitely enough.